This invention relates to valve stems for plumbing and heating valves, and more particularly to cold forming of complete headed valve stems without machining operations.
Valve stems for plumbing and heating valves are typically made of various copper alloys such as silicon brass, silicon bronze, yellow brass, red brass, DHP copper, and oxygen-free copper. The older manufacturing technique was to cast the blanks, machine them to result in the final product which comprised only about thirty percent of the original casting, the rest being scrap or recycled base. Subsequently, cold forming has been practiced, enabling successive cold heading of a workpiece blank to a desired overall configuration, followed by drilling and tapping screw holes into both axial ends. These drilling and tapping operations on both ends require costly production steps, especially since the small hole size and the "gumminess" of the metal material results in short drill and tap life.
The inventors herein conceived of a cold stamping process and product providing self-tapping holes in the axial ends of the cold headed stamping, so that drilling and tapping would not be necessary, and so that there would be no scrap/waste from machining operations, i.e., the stem would be one hundred percent net shaped. The cylindrical cavities on the axial ends could then receive self-tapping screws for assembly of the valve handle or handwheel on one end and the valve seat disc on the other end. However, efforts to stamp the holes in the head end of the workpiece resulted in unexpected problems. When the cylindrical punch was activated to punch the hole or cavity, the resulting hole would turn out off center, and/or oblong, and/or considerably larger than the punch, and often had other irregularities. For example, a cavity punched into the head end of the valve stem might be 0.700 inch deep when punched with a 0.400 inch long punch. The resulting products could not be effectively used because of these defects. Moreover, it was not at all apparent why this was occurring.
By extensive experimentation, the inventors ultimately determined how to cold form a no scrap valve stem, forming the valve stem without machining operations, and with properly sized and shaped, punched cylindrical cavities in the two axial ends thereof for receiving self-tapping screws to mount the handwheel and valve seat disc.